Spark generating device



April 14, 1959 V L. VOLPERT 2, y

SPARKGENERATING DEVICE Filed Oct. 5, 1953 Fig.1 v 1 p 2. I

United States Patent SPARK GENERATING DEVICE Ludger Volpert, Vevey, Switzerland, assignor to Jean Rochat, Lausanne, Switzerland Application October 5, 1953, Serial No. 384,201 Claims priority, application Switzerland October 6, 1952 Claims. Cl. 102-865) This invention relates to spark generating device, and more particularly to such devices adapted to be used as ignitors for explosive mixtures, such as the priming of a shell.

The main object of the invention is to provide a spark generating device wherein, upon application of a relatively low. voltage, a spark of suflicient power is immediately generated to ignite the explosive mixture.

A further object of the invention is to simplify the construction and reduce the size and the cost price of such devices.

These objects are attained by the provision of a spark generating device comprising two electrodes capable of beingconnected to the poles of a voltage source, a conductingzone disposed between the two electrodes and electrically connecting the same, said conducting zone consisting of at least one layer of a metal applied in a colloidal state to an insulating support, so that, upon application of the voltage to the electrodes, a spark immediately flashes across said conducting zone.

In a preferred embodiment of the invention the spark generating device comprises a first central rod-shaped electrode surrounded by a second cylindrical electrode and in spaced relationship therewith, and an insulating annular sleeve arranged in the space between the two electrodes, one face of this insulating annular sleeve being coated with at least one layer of colloidal metal to form a .,conducting zone between the two electrodes.

Other objects and advantages of the spark generating device according to the invention will become apparent from the following description taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a vertical axial sectional view of a spark generating device according to the invention,

Fig. 2 i'sa plan view thereof, and

Fig. 3 is an axial section of an embodiment of the invention particularly adapted to be used as an ignitor for the priming of a shell.

Figs. 1 and 2 illustrate the principles of the invention. The spark generating device consists of two electrodes 1 and 2 which are respectively connected to the poles of a voltage source T. A switch I allows the voltage of source T to be applied to the electrodes 1 and 2 of the generating device, at the desired instant, to produce a spark.

The electrodes 1 and 2 are electrically connected to each other by a conducting zone P, consisting of a layer of a metal applied in a colloidal state on an insulating support 3. The latter may also serve as a support for the electrodes 1 and 2, as shown.

If the voltage of the source T is now applied to the electrodes 1 and 2, a spark is instantaneously generated on the conducting zone P.

The voltage capable of generating this spark on the zone P is relatively low, much lower in any case than the voltage it would be necessary to provide in order to obtain a spark of the same power if, other conditions remaining constant, the metal applied to the insulating support, in-

stead of being in a colloidal state, were applied in the normal metallic state, for example by electrode-position.

An exhaustive analysis of the phenomena occurring in the colloidal layer during the flow of the current would require very involved studies which would be beyond the limits of this description and would not serve the understanding of the invention.

It is, however, possible to consider in some detail these phenomena by means of the classical knowledge concerning the colloidal state and the ionization.

It is well known that in the metal in a colloidal state the molecules are much more dispersed than in a metal in the normal state. As a result, each molecule remains in some way electrically independent and behaves as an elementary electrode. Furthermore, for a given mass of metal, the metallic free surfaces associated with the surface electric phenomena (skin effect among others) are much greater in the case of the colloidal state than in the case of the normal state, since in the colloidal state the total free surface may be assumed as the sum of the elementary surfaces of the molecules, while in the normal state the total surface is only the geometric boundary surface of the volume of the mass.

In view of the foregoing considerations, it is obvious that in the case of a colloidal metallic zone, such as zone P, a low amount of energy will suflice to produce instantaneously, within this zone and at the molecular scale, localized phenomena of ionization, which will cause the total conductivity of the zone to greatly increase. This increased conductivity will allow an immediate and very important increase of the current intensity flowing through the colloidal zone P. so that it is not necessary to increase the value of the applied voltage in order to obtain the same result. The relatively great current intensity flowing through the colloidal zone will then cause, at least locally, a dissociation of the metallic molecules followed by a new association thereof. This latter phenomenon causes a discharge of explosive nature to flash out immediately. This effect of association is well known in the theory of the explosive phenomena.

Each of the consecutive phenomena described above takes place in an infinitely short lapse of time. In this connection it is of some interest to point out that by using a conducting zone coated with colloidal silver it was possible to discharge a capacitor of about one microfarad in as short a time as a ten millionth of second, upon application of a voltage of two hundred volts at most. Obviously it would be impossible to obtain such an immediate flashing of the spark upon application of such a low voltage if the conducting zone instead of being formed with a colloidal layer were consisting of a layer of normal metal applied to the insulating support, for instance by electrodeposition or any other suitable process. In this case, the flashing of a spark would occur only after the melting of the conducting zone resulting from the heating effect of the current and this melting would require a certain lapse of time and a certain amount of energy, in other words, a high voltage and large current.

As regards the constructive details of the different elements constituting the spark generating device according to this invention, the electrodes 1 and 2 may be made either with ditferent metals (for example copper and zinc) or with the same metal (for example copper, iron, zinc, etc.).

The colloidal metallic zone P may consist of copper, gold, zinc or preferably silver, the latter material being available on the market in concentrated colloidal solutions. The procedure to be followed in order to obtain the conducting zone P comprises thinning the concentrated colloidal solution to a diluted solution and spreading it on the insulating support 3, in the area where the zone P is desired, either with a brush or by spraying.

3 The colloidal metallic layer is then dried and, if desired, the drying operation may be activated by heating. The insulating support 3 is now coated with a stable and dry layer of colloidal metal. If necessary, and according to the desired final thickness of the colloidal zone P and the extent of dilution of the solution, two or more layers of colloidal metal may be superimposed. In any case, the insulating support 3 provided with the layer of colloidal metal is subjected to a heat treatment at a temperature of a few hundred degrees centigrade, preferably within the range from 600 C. to 700 C. The purpose of this heat treatment is to obtain a perfect adhesion between the colloidal layer and the insulation support and to remove any electrostatic stress between the same.

When these operations are accomplished, a spark generating device is available which is of particularly simple and inexpensive construction, and operates instantaneously upon application of a relatively low voltage. Moreover, since the discharge deteriorates the colloidal zone only locally, it is possible to use the spark generating device many times consecutively. For this purpose it is merely necessary to regenerate the damaged zone by applying a fresh colloidal layer in the way above described.

The spark generating device according to the invention is adapted to be used in many applications and particularly in those associated with flashing lamps and electric ignition for explosive mixtures.

In Fig. 3 there is illustrated a particular embodiment of the spark generating device according to the invention, which is suitable to be used as an ignitor for the priming of a shell. The spark generating device of Fig. 3 is provided with means capable of applying the voltage of the source T to the electrodes of the generator, at the right instant. If it is desired that the explosion of the shell takes place at the very instant of the impact, the head of the shell is provided with a switch consisting of two contact elements, 4 and 5 respectively, electrically insulated between them but adapted to engage each other at the instant of the imp-act. These contact elements 4 and 5 are inserted in series in the circuit of the electrodes 1 and 2, so that under the effect of the impact, they energize the spark generating device.

The spark generating device according to Fig. 3 con sists of a first central rod-shaped electrode 1 surrounded by a second cylindrical electrode 2 in spaced'relationship therewith. An insulating annular sleeve 3 is arranged in the space between the two electrodes 1 and 2, and a face of the insulating sleeve 3 is coated with a colloidal metallic layer in the manner described above, to form the conducting zone P.

The above described arrangements are illustrative of the application of the principles of the invention. Other arrangements may be derived by those skilled in the art without departing from the spirit and scope of the invention.

Having thus described my invention, what I claim as new therein and desire to seizure by Letters Patent is:

1. An electrical discharge device particularly for use as an igniter for explosives, said device comprising spaced electrodes, an insulating support having a surface extending between said electrodes, a thin layer of colloidal metal covering an area of said surface extending from one of said electrodes to the other and consisting of 'a deposit of colloidal particles of metal produced by coating said surface area of said insulating support with a colloidal suspension of said metal and thereafter subjecting the coated support to heat, said layer forming an electrically conductive zone and being in electrical connection with said electrodes, at least one of said electrodes having an extended line of contact with said layer and said area covered by said layer having substantial width in a direction transverse to a line connecting said electrodes and means for applying a voltage differential of the order of 200 volts or less to said electrodes to produce instanta neously localized ionization of said colloidal metal to greatly increase the conductivity of said zone and cause an instantaneous discharge of explosive nature between said electrodes, said zone providing a multiplicity of electrical discharge paths between said electrodes to permit repeated discharge of said igniter. v

2. An electrical discharge device according to claim I, in which said layer of colloidal metal after being deposited has been heated to a temperature in the range of 600," C. to 700 c.

3. An electrical discharge device according to claim 1, in which said layer consists of at least one layer of colloidal silver. I I

4. An electrical discharge device according to claim 1, in which said electrodes comprise a central electrodev and an annular electrode surrounding said central electrode.

5. An electrical discharge device according to claim 4,'

in which said electrodes are fiiish with said surface of said support.

References Cited in the file of this patent UNITED STATES PATENTS 39,542 Beardslee Aug. 18, 1863 319,628 Russell "Juries, 1885 2,424,583 Rahm July 29, 1947 2,694,016 Craven et al Nov. 9, 2,719,386 Johnson et a1 Oct. 4, 1955 FOREIGN PATENTS I 122,501 Austria .e Apr. 25,- 1931 

